"Bigger Box" : is the ET relic that triggers a "contact!" but do not register damage.
"Smaller Boxes" : are the TCE hitBoxes.
- ScreenShot 1- ScreenShot 2

Here comes the HitBox with r_bonesdebug (aka tags) :

Sidenote :Forget thales about the damage, the HitBox mixed with items like FPS, Ping or Animations can explain that sometimes you shoot straight to the target and still miss to register damage.
The best thing is to do some tests by yourself.